This invention relates to electrical distribution panelboards and associated circuit protective apparatus for use in a grounded delta system. The panelboards may have main circuit breakers, main lug devices or main disconnect switch apparatus associated therewith.
Electric utility companies have for some time offered grounded delta distribution systems in certain geographical markets. The grounded delta system is a three phase, three-wire system wherein one phase of the delta configured transformer is grounded. Presently, grounded delta systems require specially rated, tested and labeled circuit protective apparatus such as circuit breakers, lugs and switches for both main and branch circuit applications. These are usually two-pole devices, but may be three-pole devices wherein only two poles are operably connected to the ungrounded phases of the delta power supply. The grounded phase of the delta power supply is connected to a neutral connector within the panelboard, and subsequently is connected from the neutral directly to the load in the respective branch circuits, bypassing the protective apparatus. Since only two phases are being opened by the protective apparatus, two poles of the apparatus handle the current and voltage that a three-pole apparatus would normally handle. The short circuit current interrupting capacity (AIC) rating of protective apparatus specifically labeled for grounded delta phase application is usually low, often much lower than such rating for the same apparatus used in a customary three-phase application. The need to manufacture and stock specially tested and labeled devices is burdensome to manufacturer, distributor and electrical contractor alike. Moreover, while two and three-pole breakers are intended to be used in a grounded delta phase panelboard, it is possible that a single pole breaker may be erroneously connected to one phase of the panel and into an available space in the conventional neutral connector, thereby inadvertently applying full transformer voltage to, for example, an outlet.